The present invention is generally directed to toner compositions and processes thereof, and more specifically, to in situ chemical toners wherein there is added to the surface thereof a first layer of metal oxide particles, preferably hydrophilic metal oxide particles, and which particles are substantially buried, or incorporated into the toner surface; and subsequently there is added a second layer thereover of metal oxide particles, wherein the second layer is preferably comprised of hydrophilic metal oxide particles or hydrophobic metal oxide particles, and which second layer particles are dispersed onto the toner surface and over the buried first metal oxide layer. The aforementioned metal oxide particles are available from a number of sources, such as Degussa Chemicals, and the first and second metal oxide particles are present as separate layers on the toner surface. The toners of the present invention can be prepared by chemical methods as indicated herein, and thereafter the first and second metal oxide surface layer additives are included by a two step blending method. With the toners of the present invention there results in embodiments excellent admix characteristics, for example the admix thereof is from about 30 seconds to about 60 seconds. The toner compositions without the additives are prepared by in situ methods, without the utilization of the known pulverization and/or classification methods, and wherein toners with an average volume diameter of from about 1 to about 25, and preferably from 1 to about 10 microns, and narrow GSD can be obtained; followed by the addition of the first metal oxide layer, and then the addition of the second metal oxide layer by, for example, known mixing methods. The resulting toners with the two metal oxide surface additive layers can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a pigment and optionally a charge control agent or additive in an aqueous mixture containing an ionic surfactant in an amount of from about 0.5 percent to about 10 percent and shearing this mixture with a latex mixture comprised of suspended resin particles of from about 0.01 micron to about 2 microns in volume average diameter in an aqueous solution containing a counterionic surfactant in amounts of from about 1 percent to about 10 percent with opposite charge to the ionic surfactant of the pigment dispersion, and nonionic surfactant in an amount of from 0 percent to about 5 percent, thereby causing a flocculation of resin particles, pigment particles and optional charge control particles, followed by stirring of the flocculent mixture, which is believed to form statically bound aggregates of from about 1 micron to about 10 microns, comprised of resin, pigment and optionally charge control particles, and thereafter, adding extra anionic or nonionic surfactant solution with a concentration of from about 5 percent to about 30 percent in the controlled amount, which will result in the overall final concentration of this surfactant in the aggregated mixture of from about 0.5 percent to about 10 percent, and preferably from 1 percent to 5 percent (weight percent throughout unless otherwise indicated) to thereby enable any further growth in particle size and GSD during the heating step, which size in embodiments is from about 3 to about 10 microns in average volume diameter, and with a GSD of from about 1.16 to about 1.26; and then heating the mixture above the polymeric resin Tg, which Tg is in range of from between about 45.degree. C. to about 90.degree. C. and preferably between about 50.degree. C. and 80.degree. C., and more preferably the resin Tg is equal to 54.degree. C., to generate toner with an average particle volume diameter of from about 1 to about 10 microns, and wherein the stirring speed in (iii) is reduced from about 300 to about 1,000 to about 100, preferably 150, to about 600 rpm, primarily to substantially eliminate fines of about 1 micron in average volume diameter, which fines can adversely affect toner yield. It is believed that during the heating stage, the components of aggregated particles fuse together to form composite toner particles. Subsequently, there is added in one step to the resulting toner a hydrophobic metal oxide layer and by a second step a top layer of a hydrophilic metal oxide.
In embodiments thereof, the present invention is directed to an in situ process comprised of first dispersing a pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., in an aqueous mixture containing a cationic surfactant, such as benzalkonium chloride (SANIZOL B-50.TM.), utilizing a high shearing device, such as a Brinkmann Polytron, or microfluidizer or sonicator, thereafter shearing this mixture with a charged latex of suspended resin particles, such as poly(styrene/butadiene/acrylic acid) or poly(styrene/butylacrylate/acrylic acid) or PLIOTONE.TM. of poly(styrene butadiene), and of particle size ranging from about 0.01 to about 0.5 micron as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an anionic surfactant, such as sodium dodecylbenzene sulfonate (for example NEOGEN R.TM. or NEOGEN SC.TM.) and nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy) ethanol (for example IGEPAL 897.TM. or ANTAROX 897.TM.), thereby resulting in a flocculation, or heterocoagulation of the resin particles with the pigment particles; and which on further stirring for from about 1 hour to about 24 hours with optional heating at from about 5.degree. to about 25.degree. C. below the resin Tg, which Tg is in the range of between 45.degree. to 90.degree. C. and preferably between about 50 and 80.degree. C., results in formation of statically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II); and adding concentrated (from about 5 percent to about 30 percent) aqueous surfactant solution containing an anionic surfactant, such as sodium dodecylbenzene sulfonate (for example NEOGEN R.TM. or NEOGEN SC.TM.) or nonionic surfactant, such as alkyl phenoxy poly(ethylenoxy) ethanol (for example IGEPAL 897.TM. or ANTAROX 897.TM.), in controlled amounts to prevent any changes in particle size, which can range from 3 to 10 microns in average volume diameter and a GSD which can range from about 1.16 to about 1.28 during the heating step, and thereafter, heating to 10 to 50.degree. C. above the resin Tg to provide for particle fusion or coalescence of the polymer and pigment particles; followed by washing with, for example, hot water to remove surfactants, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to 12 microns in average volume particle diameter, and wherein the stirring speed in (iii) is reduced in (iv) as illustrated herein. Subsequently, there is added in one step to the resulting toner a layer of hydrophilic metal oxide, wherein the layer of metal oxide is substantially buried into the toner surface, and thereafter, a second metal oxide layer is added, and which second layer is comprised of a hydrophobic metal oxide, and wherein the second metal oxide layer is dispersed onto the toner surface on top of the buried first metal oxide layer. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present. While it is not desired to be limited by theory, it is believed that the toner particles undergo plastic flow, as a result of the combination of mechanical stress and localized heating, causing the metal oxide layer to be substantially buried. The ability of the toner particles to undergo plastic flow, and thus to allow the additive layer to be buried depends, for example, on the mixing time, the mixing temperature, and on the intensity of mixing, which is controlled with a combination of agitation type, agitation rate, agitation force, and the optional addition of milling material, such as metal, plastic, or ceramic beads, and the like, such that the metal oxide layer is buried, but such that the temperature of the toner particles remains at least 5.degree. C., and preferably more than 10.degree. C. below the toner Tg so that agglomeration of the toner particles is substantially avoided. Thereafter, a second metal oxide layer is added, and which second layer is comprised of a hydrophobic metal oxide, or a hydrophilic metal oxide, and wherein the second metal oxide layer is dispersed onto the toner surface on top of the buried first metal oxide layer. By reducing the blending time, the blending temperature, and optionally reducing the blending intensity, the second additive layer is not substantially buried into the toner surface. While it is not desired to be limited by theory, it is believed that in the second step, that the toner particles do not undergo sufficient plastic flow, as a result of the combination of mechanical stress and localized heating, preventing any substantial amount of metal oxide from being buried into the toner surface. The intensity of mixing is reduced with a combination of reduced agitation rate, reduced agitation force, changing the agitation type, removing or reducing the amount of optional milling material, or the milling material, such as metal, plastic, or ceramic beads, and the like, such that the metal oxide layer is not substantially buried. In addition, it is important that the temperature of the toner particles remains at least 5.degree. C. below the toner Tg, and preferably more than 10.degree. C. below the toner Tg, so that agglomeration of the toner particles, and burying of the additive is substantially avoided.
Toners with fumed silica surface additives are known, reference for example U.S. Pat. No. 3,900,588, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 3,983,045 developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43. Toners with silica like AEROSIL.RTM. are also known.
There is illustrated in U.S. Pat. No. 4,996,127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of this '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. In U.S. Pat. No. 4,983,488, there is illustrated a process for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. Similarly, the aforementioned disadvantages are noted in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent polar resins of opposite charges are selected.
Illustrated in copending patent applications U.S. Ser. No. 331,444 and U.S. Ser. No. 331,441, now U.S. Pat. Nos. 5,486,443 and 5,482,805, respectively, the disclosures of which are totally incorporated herein by reference, are toners with surface additive mixtures of silica, polyvinylidene fluoride, a KYNAR.RTM., and strontium titanate.
The toner compositions of the present invention, prior to the addition of metal oxide layers, are preferably prepared by chemical methods, and more specifically, by emulsion/aggregation methods as illustrated in U.S. Pat. Nos. 5,418,108; 5,370,963; 5,344,738; 5,403,693; 5,364,729 and 5,405,728, the disclosures of which are totally incorporated herein by reference. In U.S. Pat. No. 5,370,963, there is illustrated a process for the preparation of toner compositions with controlled particle size comprising:
(i) preparing a pigment dispersion in water, which dispersion is comprised of pigment, an ionic surfactant and an optional charge control agent; PA1 (ii) shearing at high speeds the pigment dispersion with a polymeric latex comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, and a nonionic surfactant thereby forming a uniform homogeneous blend dispersion comprised of resin, pigment, and optional charge agent; PA1 (iii) heating the above sheared homogeneous blend below about the glass transition temperature (Tg) of the resin while continuously stirring to form electrostatically bound toner size aggregates with a narrow particle size distribution; PA1 (iv) heating the statically bound aggregated particles above about the Tg of the resin particles to provide coalesced toner comprised of resin, pigment and optional charge control agent, and subsequently optionally accomplishing (v) and (vi); PA1 (v) separating said toner; and PA1 (vi) drying said toner. PA1 (i) preparing a pigment dispersion, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent; PA1 (ii) shearing said pigment dispersion with a latex or emulsion blend comprised of resin, a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant and a nonionic surfactant; PA1 (iii) heating the above sheared blend below about the glass transition temperature (Tg) of the resin to form electrostatically bound toner size aggregates with a narrow particle size distribution; and PA1 (iv) heating said bound aggregates above about the Tg of the resin. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant, and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin, and charge control agent; PA1 (iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution; PA1 (iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute, and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); PA1 (v) heating and coalescing from about 5 to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. C. to about 90.degree. C. and preferably from between about 50.degree. C. and about 80.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent; PA1 (vi) washing the aggregated particles at a temperature of from about 15.degree. C. to about 5.degree. C. below the glass transition temperature of the resin, and subsequently filtering the aggregated particles until substantially all of the surfactant has been removed from the aggregated particles, followed by subsequent drying of the particles at a temperature of from about 15.degree. C. to about 5.degree. C. below the glass transition temperature of the resin; and PA1 (vii) subsequently adding to said toner product a first layer of a hydrophilic metal oxide, and a second layer of a hydrophobic metal oxide; and wherein the thickness of the first layer of a hydrophilic metal oxide is from about 10 nanometers to about 200 nanometers, whereby the metal oxide occupies about 10 percent to about 80 percent of the volume of said layer, and the thickness of the second layer of a metal oxide is from about 10 nanometers to about 200 nanometers, whereby the metal oxide covers about 20 percent to about 100 percent of the area of the toner surface; and a process for the preparation of toner compositions with controlled particle size comprising: PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment, an ionic surfactant in amounts of from about 0.5 to about 10 percent by weight of water, and an optional charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant, and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin, and charge control agent; PA1 (iii) stirring the resulting sheared viscous mixture of (ii) at from about 300 to about 1,000 revolutions per minute to form electrostatically bound substantially stable toner size aggregates with a narrow particle size distribution; PA1 (iv) reducing the stirring speed in (iii) to from about 100 to about 600 revolutions per minute, and subsequently adding further anionic or nonionic surfactant in the range of from about 0.1 to about 10 percent by weight of water to control, prevent, or minimize further growth or enlargement of the particles in the coalescence step (iii); PA1 (v) heating and coalescing from about 5 to about 50.degree. C. above about the resin glass transition temperature, Tg, which resin Tg is from between about 45.degree. C. to about 90.degree. C., the statically bound aggregated particles to form said toner composition comprised of resin, pigment and optional charge control agent; PA1 (vi) washing the aggregated particles at a temperature of from about 15.degree. C. to about 5.degree. C. below the glass transition temperature of the resin, and subsequently filtering the aggregated particles until substantially all of the surfactant has been removed from the aggregated particles, followed by subsequent drying of the particles at a temperature of from about 15.degree. C. to about 5.degree. C. below the glass transition temperature of the resin; and PA1 (vii) subsequently adding to said toner product a first layer of a hydrophilic oxide, and a second layer of a hydrophobic oxide.
In U.S. Pat. No. 5,364,797, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions comprising: